X-ray powder diffractometry is a commonly used analytical technique for identifying the structure of a material. Fundamentally, the procedure involves directing a small beam of monochromatic X-rays into a polycrystalline sample and then recording the resultant pattern of diffracted X-rays as diffraction signal peaks on film or using a detector. Since different substances produce unique diffraction patterns due to their atomic arrangement, this technique serves as a “fingerprint” for identification of both known and unknown materials.
General sample preparation for X-ray powder diffractometry involves placing a powder sample into a sample holder which is then inserted into the X-ray powder diffractometer. The design of the sample holder is important for both ease of use and for obtaining the best analytical results. For example, collection of the desired data is enhanced if the sample holder is constructed of material which does not produce strong background signal intensity which may alter or conceal small peaks caused by the sample. If the construction material of the sample holder does produce large diffraction peaks, it is preferred that the large diffraction peaks not be in the vicinity of the diffraction peaks of interest from the sample.
Traditionally, a sample holder for X-ray powder diffractometry would contain a single sample for analysis, with sample changers being used to analyze multiple samples in sequence. However, with the growth of combinatorial approaches to the synthesis of new materials, a need has arisen for handling and preparing arrays of samples for analysis. The most efficient techniques are those that manipulate entire arrays of samples in parallel as opposed to manipulating samples individually, i.e., one at a time. One such approach is documented in Choi, Kwangwook; Gardner, David; Hilbrandt, Nicole, Bein, Thomas, Angew. Chem. Int. Ed. 1999, 38, No. 19, 2891-94 where products from hydrothermal synthesis are washed and isolated as an array using a custom-designed centrifuge apparatus and the samples are collected on filter paper and transferred to a sample holder for X-ray analysis. The custom-designed centrifuge apparatus consisted of two different filter papers, glass microfiber and normal filter paper, a PVC main support with a matching hold pattern, a filtrate reservoir and a PVC cylinder. Two pieces of filter paper were placed between the multiclave hydrothermal synthesis vessel and the PVC main support that was connected to the filtrate reservoir. For washing, the multiclave and the PVC main support were turned upside down, and water was added into the holes of the PVC main support and then forced into the multiclave by centrifugation. The steps were repeated several times.
Another approach is disclosed in Klein, Jens; Lehmann, Christian W.; Schmidt, Hans-Werner; Maier, Wilhelm F. Angew. Chem. Int. Ed. 1998 37, No. 24, 3369-72 where the bottom of a multiclave synthesis vessel is a silicon wafer. Upon completion of the reaction in an autoclave and cooling, reaction solution was removed from the solids using small porous rods with the solids remaining on the surface of the silicon wafer. The product was washed several times directly in the multiclave synthesis vessel and heated to remove the moisture. The silicon wafer with dried-on crystals was removed and calcined and the products sintered onto the silicon wafer. The silicon wafer was mounted in the X-ray diffractometer and the beam was focussed at the location of each individual spot of sample.
The invention disclosed herein, however, provides a process and apparatus for preparing an array of samples where each sample has a flat surface at a predefined location and where the flat surfaces are in a common plane. The sample preparation of the present invention allows for the sample holder containing the array of samples to be positioned within an X-ray powder diffractometer in a matter of seconds and the array of samples to be analyzed in a very efficient manner.